Early cystic fibrosis lung disease: Role of airway surface dehydration and lessons from preventive rehydration therapies in mice

[Chronic rhinosinusitis in people with cystic fibrosis-an up-to-date review from the perspective of otorhinolaryngology]

BACKGROUND

Cystic fibrosis (CF) is a complex systemic disease involving numerous organ systems. With improved treatment options and increasing life expectancy of persons with CF (PwCF), extrapulmonary manifestations are coming increasingly into the focus. From birth, almost all PwCF have radiologically detectable pathologies in the upper airways attributable to CF-associated chronic rhinosinusitis (CF-CRS).

OBJECTIVE

The aim of this work is to provide an up-to-date overview of CF-CRS from the otorhinolaryngology perspective and to provide the reader with background knowledge and current developments.

PATHOPHYSIOLOGY

The cystic fibrosis transmembrane conductance regulator (CFTR) gene defect leads to increased viscosity of sinonasal secretions and reduced mucociliary clearance, causing chronic infection and inflammation in the upper airway segment and, consequently, to CF-CRS.

CLINICAL PICTURE AND DIAGNOSTICS

The clinical picture of CF-CRS comprises a wide spectrum from asymptomatic to symptomatic courses. CF-CRS is diagnosed clinically and radiologically.

THERAPY

Sinonasal saline irrigation is recommended as a conservative treatment measure. Topical corticosteroids are also commonly used. Surgical therapy is reserved for highly symptomatic treatment-refractory patients without a sufficient response to conservative treatment including CFTR modulator (CFTRm) therapies. Depending on the CFTR mutation, CFTRm therapies are the treatment of choice. They not only improve the pulmonary and gastrointestinal manifestations in PwCF, but also have positive effects on CF-CRS.

CONCLUSION

The ENT specialist is part of the interdisciplinary team caring for PwCF. Depending on symptom burden and treatment responsiveness, CF-CRS should be treated conservatively and/or surgically. Modern CFTRm have a positive effect on the clinical course of CF-CRS.

Abnormal functional lymphoid tolerance and enhanced myeloid exocytosis are characteristics of resting and stimulated PBMCs in cystic fibrosis patients

Introduction

Cystic Fibrosis (CF) is the commonest genetically inherited disease (1 in 4,500 newborns) and 70% of people with CF (pwCF) harbour the F508Del mutation, resulting in misfolding and incorrect addressing of the channel CFTR to the epithelial membrane and subsequent dysregulation of fluid homeostasis. Although studies have underscored the importance and over-activation of myeloid cells, and in particular neutrophils in the lungs of people with CF (pwCF), relatively less emphasis has been put on the potential immunological bias in CF blood cells, at homeostasis or following stimulation/infection.

Methods

Here, we revisited, in an exhaustive fashion, in pwCF with mild disease (median age of 15, median % FEV1 predicted = 87), whether their PBMCs, unprimed or primed with a 'non specific' stimulus (PMA+ionomycin mix) and a 'specific' one (live P.a =PAO1 strain), were differentially activated, compared to healthy controls (HC) PBMCs.

Results

1) we analysed the lymphocytic and myeloid populations present in CF and Control PBMCs (T cells, NKT, Tgd, ILCs) and their production of the signature cytokines IFN-g, IL-13, IL-17, IL-22. 2) By q-PCR, ELISA and Luminex analysis we showed that CF PBMCs have increased background cytokines and mediators production and a partial functional tolerance phenotype, when restimulated. 3) we showed that CF PBMCs low-density neutrophils release higher levels of granule components (S100A8/A9, lactoferrin, MMP-3, MMP-7, MMP-8, MMP-9, NE), demonstrating enhanced exocytosis of potentially harmful mediators.

Discussion

In conclusion, we demonstrated that functional lymphoid tolerance and enhanced myeloid protease activity are key features of cystic fibrosis PBMCs.

SNSP113 (PAAG) improves mucociliary transport and lung pathology in the Scnn1b-Tg murine model of CF lung disease

BACKGROUND

Mucus stasis, a hallmark of muco-obstructive disease, results from impaired mucociliary transport and leads to lung function decline and chronic infection. Although therapeutics that target mucus stasis in the airway, such as hypertonic saline or rhDNAse, show some therapeutic benefit, they do not address the underlying electrostatic defect apparent in mucins in CF and related conditions. We have previously shown poly (acetyl, arginyl) glucosamine (PAAG, developed as SNSP113), a soluble, cationic polymer, significantly improves mucociliary transport in a rat model of CF by normalizing the charge defects of CF mucin. Here, we report efficacy in the CFTR-sufficient, ENaC hyperactive, Scnn1b-Tg mouse model that develops airway muco-obstruction due to sodium hyperabsorption and airway dehydration.

METHODS

Scnn1b-Tg mice were treated with either 250 µg/mL SNSP113 or vehicle control (1.38% glycerol in PBS) via nebulization once daily for 7 days and then euthanized for analysis. Micro-Optical Coherence Tomography-based evaluation of excised mouse trachea was used to determine the effect on the functional microanatomy. Tissue analysis was performed by routine histopathology.

RESULTS

Nebulized treatment of SNSP113 significantly improved mucociliary transport in the airways of Scnn1b-Tg mice, without altering the airway surface or periciliary liquid layer. In addition, SNSP113 significantly reversed epithelial hypertrophy and goblet cell metaplasia. Finally, SNSP113 significantly ameliorated eosinophilic crystalline pneumonia and lung consolidation in addition to inflammatory macrophage influx in this model.

CONCLUSION

Overall, this study extends the efficacy of SNSP113 as a potential therapeutic to alleviate mucus stasis in muco-obstructive diseases in CF and potentially in related conditions.

A novel thiol-saccharide mucolytic for the treatment of muco-obstructive lung diseases

BACKGROUND

Mucin disulfide cross-links mediate pathologic mucus formation in muco-obstructive lung diseases. MUC-031, a novel thiol-modified carbohydrate compound, cleaves disulfides to cause mucolysis. The aim of this study was to determine the mucolytic and therapeutic effects of MUC-031 in sputum from patients with cystic fibrosis (CF) and mice with muco-obstructive lung disease (βENaC-Tg mice).

METHODS

We compared the mucolytic efficacy of MUC-031 and existing mucolytics (N-acetylcysteine (NAC) and recombinant human deoxyribonuclease I (rhDNase)) using rheology to measure the elastic modulus (G') of CF sputum, and we tested effects of MUC-031 on airway mucus plugging, inflammation and survival in βENaC-Tg mice to determine its mucolytic efficacy in vivo.

RESULTS

In CF sputum, compared to the effects of rhDNase and NAC, MUC-031 caused a larger decrease in sputum G', was faster in decreasing sputum G' by 50% and caused mucolysis of a larger proportion of sputum samples within 15 min of drug addition. Compared to vehicle control, three treatments with MUC-031 in 1 day in adult βENaC-Tg mice decreased airway mucus content (16.8±3.2 versus 7.5±1.2 nL·mm-2, p<0.01) and bronchoalveolar lavage cells (73 833±6930 versus 47 679±7736 cells·mL-1, p<0.05). Twice-daily treatment with MUC-031 for 2 weeks also caused decreases in these outcomes in adult and neonatal βENaC-Tg mice and reduced mortality from 37% in vehicle-treated βENaC-Tg neonates to 21% in those treated with MUC-031 (p<0.05).

CONCLUSION

MUC-031 is a potent and fast-acting mucolytic that decreases airway mucus plugging, lessens airway inflammation and improves survival in βENaC-Tg mice. These data provide rationale for human trials of MUC-031 in muco-obstructive lung diseases.

Intravital imaging of mucus transport in asthmatic mice using microscopic optical coherence tomography

Asthma is one of the most common chronic diseases. Mucus overproduction is consistently linked to asthma morbidity and mortality. Despite the knowledge of the importance of mucus, little data exists on how mucus is transported in asthma and the immediate effects of therapeutic intervention. We therefore used microscopic optical coherence tomography (mOCT) to study spontaneous and induced mucus transport in an interleukin-13 (IL-13) induced asthma mouse model and examined the effects of isotonic (0.9% NaCl) and hypertonic saline (7% NaCl) which are used to induce mucus transport in cystic fibrosis. Without intervention, no bulk mucus transport was observed by mOCT and no intraluminal mucus was detectable in the intrapulmonary airways by histology. Administration of ATP-g-S induced mucus secretion into the airway lumen, but did not result in bulk mucus transport in the trachea. Intraluminal secreted immobile mucus could be mobilized by administration of isotonic or hypertonic saline but hypertonic saline mobilized mucus more reliably than isotonic saline. Irrespective of saline concentration, the mucus was transported in mucus chunks. In contrast to isotonic saline solution, hypertonic saline solution alone was able to induce mucus secretion. In conclusion, mOCT is suitable to examine the effects of mucus-mobilizing therapies in vivo. Although hypertonic saline was more efficient in inducing mucus transport, it induced mucus secretion, which might explain its limited benefit in asthma patients.

Multicentre feasibility of multiple-breath washout in preschool children with cystic fibrosis and other lung diseases

Background

Multiple-breath washout (MBW)-derived lung clearance index (LCI) detects early cystic fibrosis (CF) lung disease. LCI was used as an end-point in single- and multicentre settings at highly experienced MBW centres in preschool children. However, multicentre feasibility of MBW in children aged 2–6 years, including centres naïve to this technique, has not been determined systematically.

Methods

Following central training, 91 standardised nitrogen MBW investigations were performed in 74 awake preschool children (15 controls, 46 with CF, and 13 with other lung diseases), mean age 4.6±0.9 years at investigation, using a commercially available device across five centres in Germany (three experienced, two naïve to the performance in awake preschool children) with central data analysis. Each MBW investigation consisted of several measurements.

Results

Overall success rate of MBW investigations was 82.4% ranging from 70.6% to 94.1% across study sites. The number of measurements per investigation was significantly different between sites ranging from 3.7 to 6.2 (p<0.01), while the mean number of successful measurements per investigation was comparable with 2.1 (range, 1.9 to 2.5; p=0.46). In children with CF, the LCI was increased (median 8.2, range, 6.7–15.5) compared to controls (median 7.3, range 6.5–8.3; p<0.01), and comparable to children with other lung diseases (median 7.9, range, 6.6–13.9; p=0.95).

Conclusion

This study demonstrates that multicentre MBW in awake preschool children is feasible, even in centres previously naïve, with central coordination to assure standardised training, quality control and supervision. Our results support the use of LCI as multicentre end-point in clinical trials in awake preschoolers with CF.

MBW is feasible in awake preschool children with high success rates in a multicentre setting and LCI detects ventilation inhomogeneity in preschool children with CF. This supports LCI as an end-point in early intervention trials in preschool children with CF.https://bit.ly/3lD4wnj

[Clinical presentation of lung disease in cystic fibrosis]

Although cystic fibrosis (CF) is a multiorgan disease, the extent of CF lung disease is decisive for the course and survival of patients. The optimization of symptomatic therapies has led to a significant improvement in the life expectancy of those affected in recent decades. Regular monitoring of the course of CF lung disease with microbiological, pulmonary function, and imaging examinations is essential for early detection of problems and individualized therapy. With new, causal therapy options in the form of cystic fibrosis transmembrane conductance regulator (CFTR) modulators and early diagnosis through newborn screening, a further normalization of life expectancy and quality of life of CF patients can be expected.

Intravital microscopic optical coherence tomography imaging to assess mucus-mobilizing interventions for muco-obstructive lung disease in mice

Airway mucus obstruction is a hallmark of chronic lung diseases such as cystic fibrosis, asthma, and COPD, and the development of more effective mucus-mobilizing therapies remains an important unmet need for patients with these muco-obstructive lung diseases. However, methods for sensitive visualization and quantitative assessment of immediate effects of therapeutic interventions on mucus clearance in vivo are lacking. In this study, we determined whether newly developed high-speed microscopic optical coherence tomography (mOCT) is sensitive to detect and compare in vivo effects of inhaled isotonic saline, hypertonic saline, and bicarbonate on mucus mobilization and clearance in Scnn1b-transgenic mice with muco-obstructive lung disease. In vivo mOCT imaging showed that inhaled isotonic saline-induced rapid mobilization of mucus that was mainly transported as chunks from the lower airways of Scnn1b-transgenic mice. Hypertonic saline mobilized a significantly greater amount of mucus that showed a more uniform distribution compared with isotonic saline. The addition of bicarbonate-to-isotonic saline had no effect on mucus mobilization, but also led to a more uniform mucus layer compared with treatment with isotonic saline alone. mOCT can detect differences in response to mucus-mobilizing interventions in vivo, and may thus support the development of more effective therapies for patients with muco-obstructive lung diseases.

An Improved Inhaled Mucolytic to Treat Airway Muco-obstructive Diseases

RATIONALE

Airways obstruction with thick, adherent mucus is a pathophysiologic and clinical feature of muco-obstructive respiratory diseases, including chronic obstructive pulmonary disease, asthma, and cystic fibrosis (CF). Mucins, the dominant biopolymer in mucus, organize into complex polymeric networks via the formation of covalent disulfide bonds, which govern the viscoelastic properties of the mucus gel. For decades, inhaled N-acetylcysteine (NAC) has been used as a mucolytic to reduce mucin disulfide bonds with little, if any, therapeutic effects. Improvement of mucolytic therapy requires the identification of NAC deficiencies and the development of compounds that overcome them.

OBJECTIVES

Elucidate the pharmacological limitations of NAC and test a novel mucin-reducing agent, P3001, in preclinical settings.

METHODS

The study used biochemical (e.g., Western blotting, mass spectrometry) and biophysical assays (e.g., microrheology/macrorheology, spinnability, mucus velocity measurements) to test compound efficacy and toxicity in in vitro and in vivo models and patient sputa.

MEASUREMENTS AND MAIN RESULTS

Dithiothreitol and P3001 were directly compared with NAC in vitro and both exhibited superior reducing activities. In vivo, P3001 significantly decreased lung mucus burden in βENaC-overexpressing mice, whereas NAC did not (n = 6-24 mice per group). In NAC-treated CF subjects (n = 5), aerosolized NAC was rapidly cleared from the lungs and did not alter sputum biophysical properties. In contrast, P3001 acted faster and at lower concentrations than did NAC, and it was more effective than DNase in CF sputum ex vivo.

CONCLUSIONS

These results suggest that reducing the viscoelasticity of airway mucus is an achievable therapeutic goal with P3001 class mucolytic agents.

The epithelial sodium channel (ENaC) as a therapeutic target for cystic fibrosis

Cystic fibrosis (CF) is a monogenic disease caused by mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene. CFTR dysfunction is characterized by abnormal mucociliary transport due to a dehydrated airway surface liquid (ASL) and hyperviscous mucus, among other pathologies of host defense. ASL depletion is caused by the absence of CFTR mediated chloride secretion along with continued activity of the epithelial sodium channel (ENaC) activity, which can also be affected by CFTR mediated anion conductance. Therefore, ENaC has been proposed as a therapeutic target to ameliorate ASL dehydration and improve mucus transport. Inhibition of ENaC has been shown to restore ASL hydration and enhance mucociliary transport in induced models of CF lung disease. To date, no therapy inhibiting ENaC has successfully translated to clinical efficacy, in part due to concerns regarding off-target effects, systemic exposure, durability of effect, and adverse effects. Recent efforts have been made to develop novel, rationally designed therapeutics to produce-specific, long-lasting inhibition of ENaC activity in the airways while simultaneously minimizing off target fluid transport effects, systemic exposure and side effects. Such approaches comprise next-generation small molecule direct inhibitors, indirect channel-activating protease inhibitors, synthetic peptide analogs, and oligonucleotide-based therapies. These novel therapeutics represent an exciting step forward in the development of ENaC-directed therapies for CF.

Comparison of lung clearance index determined by washout of N2 and SF6 in infants and preschool children with cystic fibrosis

BACKGROUND

Multiple-breath washout (MBW) has been shown to detect early impairment of lung function in children with cystic fibrosis (CF). Nitrogen (N₂) or sulfur hexafluoride (SF₆) can be used as tracer gas for MBW. Recent data indicated higher lung clearance index (LCI) values measured with N₂-MBW than concurrent SF₆-MBW in older children and adults, however, a comparison in infants and younger children, as well as to other outcome measures of CF lung disease is pending.

METHODS

N₂- and SF₆-MBW were performed consecutively in 31 sedated infants and preschool children with CF (mean age, 2.3 ± 0.8 years) and 20 controls (mean age, 2.3 ± 1.1 years) using the Exhalyzer D system. Children with CF also underwent chest magnetic resonance imaging (MRI).

RESULTS

Mean difference (95% CI) in LCI between N₂- and SF₆-MBW was 1.1 ± 0.4 (0.9 to 1.3) in controls and 2.1 ± 1.9 (1.4 to 2.8) in CF. Agreement between N₂- and SF₆-LCI was poor in children with CF. N₂-LCI and SF₆-LCI correlated with MRI, however N₂-LCI showed a higher concordance with MRI than SF₆-LCI. The absolute difference between N₂- and SF₆-LCI values increased with the severity of CF lung disease as determined by MRI scores.

CONCLUSION

N₂-LCI values were higher than SF₆-LCI values in infants and preschool children with CF and controls. Better concordance of N₂-LCI than SF₆-LCI with chest MRI scores point towards of a higher sensitivity of N₂-LCI to detect early lung disease in children with CF.

Three-center feasibility of lung clearance index in infants and preschool children with cystic fibrosis and other lung diseases

BACKGROUND

Lung clearance index (LCI) detects early ventilation inhomogeneity and has been suggested as sensitive endpoint in multicenter intervention trials in infants and preschoolers with cystic fibrosis (CF). However, the feasibility of multicenter LCI in this age group has not been determined. We, therefore, investigated the feasibility of LCI in infants and preschoolers with and without CF in a three-center setting.

METHODS

Following central training, standardized SF₆-MBW measurements were performed in 73 sedated children (10 controls, 49 with CF and 14 with other lung diseases), mean age 2.3±1.2years across three centers, and data were analyzed centrally.

RESULTS

Overall success rate of LCI measurements was 91.8% ranging from 78.9% to 100% across study sites. LCI was increased in patients with CF (P<0.05) and with other lung diseases (P<0.05) compared to controls.

CONCLUSION

Our results support feasibility of LCI as multicenter endpoint in clinical trials in infants and preschoolers with CF.

SPX-101 Is a Novel Epithelial Sodium Channel-targeted Therapeutic for Cystic Fibrosis That Restores Mucus Transport

RATIONALE

Cystic fibrosis (CF) lung disease is caused by the loss of function of the cystic fibrosis transmembrane conductance regulator (CFTR) combined with hyperactivation of the epithelial sodium channel (ENaC). In the lung, ENaC is responsible for movement of sodium. Hyperactivation of ENaC, which creates an osmotic gradient that pulls fluid out of the airway, contributes to reduced airway hydration, causing mucus dehydration, decreased mucociliary clearance, and recurrent acute bacterial infections. ENaC represents a therapeutic target to treat all patients with CF independent of their underlying CFTR mutation.

OBJECTIVES

To investigate the in vitro and in vivo efficacy of SPX-101, a peptide mimetic of the natural regulation of ENaC activity by short palate, lung, and nasal epithelial clone 1, known as SPLUNC1.

METHODS

ENaC internalization by SPX-101 in primary human bronchial epithelial cells from healthy and CF donors was assessed by surface biotinylation and subsequent Western blot analysis. SPX-101's in vivo therapeutic effect was assessed by survival of β-ENaC-transgenic mice, mucus transport in these mice, and mucus transport in a sheep model of CF.

MEASUREMENTS AND MAIN RESULTS

SPX-101 binds selectively to ENaC and promotes internalization of the α-, β-, and γ-subunits. Removing ENaC from the membrane with SPX-101 causes a significant decrease in amiloride-sensitive current. The peptide increases survival of β-ENaC-transgenic mice to greater than 90% with once-daily dosing by inhalation. SPX-101 increased mucus transport in the β-ENaC mouse model as well as the sheep model of CF.

CONCLUSIONS

These data demonstrate that SPX-101 promotes durable reduction of ENaC membrane concentration, leading to significant improvements in mucus transport.

Progress in understanding mucus abnormalities in cystic fibrosis airways

Normal airways below the carina maintain an essentially sterile environment via a multi-pronged innate defence system that includes mucus clearance via mucociliary clearance and cough, multiple antimicrobials and cellular components including macrophages and neutrophils. In cystic fibrosis (CF), loss of CFTR function compromises these defences, and with present standard of care virtually all people with CF eventually develop mucus accumulation, plugging and chronic infections. This review focuses on how mucus is affected by CFTR loss.

The development of lower respiratory tract microbiome in mice

BACKGROUND

Although culture-independent methods have paved the way for characterization of the lung microbiome, the dynamic changes in the lung microbiome from neonatal stage to adult age have not been investigated.

RESULTS

In this study, we tracked changes in composition and diversity of the lung microbiome in C57BL/6N mice, starting from 1-week-old neonates to 8-week-old mice. Towards this, the lungs were sterilely excised from mice of different ages from 1 to 8 weeks. High-throughput DNA sequencing of the 16S rRNA gene followed by composition and diversity analysis was utilized to decipher the microbiome in these samples. Microbiome analysis suggests that the changes in the lung microbiome correlated with age. The lung microbiome was primarily dominated by phyla Proteobacteria, Firmicutes, Bacteroidetes, and Actinobacteria in all the stages from week 1 to week 8 after birth. Although Defluvibacter was the predominant genus in 1-week-old neonatal mice, Streptococcus became the dominant genus at the age of 2 weeks. Lactobacillus, Defluvibacter, Streptococcus, and Achromobacter were the dominant genera in 3-week-old mice, while Lactobacillus and Achromobacter were the most abundant genera in 4-week-old mice. Interestingly, relatively greater diversity (at the genus level) during the age of 5 to 6 weeks was observed as compared to the earlier weeks. The diversity of the lung microbiome remained stable between 6 and 8 weeks of age.

CONCLUSIONS

In summary, we have tracked the development of the lung microbiome in mice from an early age of 1 week to adulthood. The lung microbiome is dominated by the phyla Proteobacteria, Firmicutes, Bacteroidetes, and Actinobacteria. However, dynamic changes were observed at the genus level. Relatively higher richness in the microbial diversity was achieved by age of 6 weeks and then maintained at later ages. We believe that this study improves our understanding of the development of the mice lung microbiome and will facilitate further analyses of the role of the lung microbiome in chronic lung diseases.

Lung function imaging methods in Cystic Fibrosis pulmonary disease

Monitoring of pulmonary physiology is fundamental to the clinical management of patients with Cystic Fibrosis. The current standard clinical practise uses spirometry to assess lung function which delivers a clinically relevant functional readout of total lung function, however does not supply any visible or localised information. High Resolution Computed Tomography (HRCT) is a well-established current 'gold standard' method for monitoring lung anatomical changes in Cystic Fibrosis patients. HRCT provides excellent morphological information, however, the X-ray radiation dose can become significant if multiple scans are required to monitor chronic diseases such as cystic fibrosis. X-ray phase-contrast imaging is another emerging X-ray based methodology for Cystic Fibrosis lung assessment which provides dynamic morphological and functional information, albeit with even higher X-ray doses than HRCT. Magnetic Resonance Imaging (MRI) is a non-ionising radiation imaging method that is garnering growing interest among researchers and clinicians working with Cystic Fibrosis patients. Recent advances in MRI have opened up the possibilities to observe lung function in real time to potentially allow sensitive and accurate assessment of disease progression. The use of hyperpolarized gas or non-contrast enhanced MRI can be tailored to clinical needs. While MRI offers significant promise it still suffers from poor spatial resolution and the development of an objective scoring system especially for ventilation assessment.

Airway mucus, inflammation and remodeling: emerging links in the pathogenesis of chronic lung diseases

Airway mucus obstruction is a hallmark of many chronic lung diseases including rare genetic disorders such as cystic fibrosis (CF) and primary ciliary dyskinesia, as well as common lung diseases such as asthma and chronic obstructive pulmonary disease (COPD), which have emerged as a leading cause of morbidity and mortality worldwide. However, the role of excess airway mucus in the in vivo pathogenesis of these diseases remains poorly understood. The generation of mice with airway-specific overexpression of epithelial Na⁺ channels (ENaC), exhibiting airway surface dehydration (mucus hyperconcentration), impaired mucociliary clearance (MCC) and mucus plugging, led to a model of muco-obstructive lung disease that shares key features of CF and COPD. In this review, we summarize recent progress in the understanding of causes of impaired MCC and in vivo consequences of airway mucus obstruction that can be inferred from studies in βENaC-overexpressing mice. These studies confirm that mucus hyperconcentration on airway surfaces plays a critical role in the pathophysiology of impaired MCC, mucus adhesion and airway plugging that cause airflow obstruction and provide a nidus for bacterial infection. In addition, these studies support the emerging concept that excess airway mucus per se, probably via several mechanisms including hypoxic epithelial necrosis, retention of inhaled irritants or allergens, and potential immunomodulatory effects, is a potent trigger of chronic airway inflammation and associated lung damage, even in the absence of bacterial infection. Finally, these studies suggest that improvement of mucus clearance may be a promising therapeutic strategy for a spectrum of muco-obstructive lung diseases.

Hypoxia and sterile inflammation in cystic fibrosis airways: mechanisms and potential therapies

Cystic fibrosis is one of the most common autosomal recessive genetic diseases in Caucasian populations. Diagnosisvianewborn screening and targeted nutritional and antibiotic therapy have improved outcomes, however respiratory failure remains the key cause of morbidity and mortality. Progressive respiratory disease in cystic fibrosis is characterised by chronic neutrophilic airway inflammation associated with structural airway damage leading to bronchiectasis and decreased lung function. Mucus obstruction is a characteristic early abnormality in the cystic fibrosis airway, associated with neutrophilic inflammation often in the absence of detectable infection. Recent studies have suggested a link between hypoxic cell death and sterile neutrophilic inflammation in cystic fibrosis and other diseasesviathe IL-1 signalling pathway. In this review, we consider recent evidence regarding the cellular responses to respiratory hypoxia as a potential driver of sterile neutrophilic inflammation in the lung, current knowledge on hypoxia as a pathogenic mechanism in cystic fibrosis and the potential for current and future therapies to alleviate hypoxia-driven sterile inflammation.

Neutrophil elastase and matrix metalloproteinase 12 in cystic fibrosis lung disease

Chronic lung disease remains the major cause of morbidity and mortality in patients with cystic fibrosis (CF). Recent studies in young children with CF diagnosed by newborn screening identified neutrophil elastase (NE), a major product released from neutrophils in inflamed airways, as a key risk factor for the onset and early progression of CF lung disease. However, the understanding of how NE and potentially other proteases contribute to the complex in vivo pathogenesis of CF lung disease remains limited. In this review, we summarize recent progress in this area based on studies in βENaC-overexpressing (βENaC-Tg) mice featuring CF-like lung disease and novel protease-specific Förster resonance energy transfer (FRET) sensors for localization and quantification of protease activity in the lung. These studies demonstrated that NE is implicated in several key features of CF lung disease such as neutrophilic airway inflammation, mucus hypersecretion, and structural lung damage in vivo. Furthermore, these studies identified macrophage elastase (matrix metalloproteinase 12 (MMP12)) as an additional protease contributing to early lung damage in βENaC-Tg mice. Collectively, these results suggest that NE and MMP12 released from activated neutrophils and macrophages in mucus-obstructed airways play important pathogenetic roles and may serve as potential therapeutic targets to prevent and/or delay irreversible structural lung damage in patients with CF.

Early detection and sensitive monitoring of CF lung disease: Prospects of improved and safer imaging

Recent imaging studies using chest computed tomography (CT) in presymptomatic infants and young children with cystic fibrosis (CF) diagnosed by newborn screening presented compelling evidence of early onset and progression of structural lung damage in CF. These data argue persuasively that non-invasive outcome measures for early detection and sensitive monitoring of lung disease applicable in the clinical setting will be instrumental for further improvement of clinical care and the development of early intervention therapies that have the potential to prevent irreversible lung damage. In this context, the use of CT imaging for early detection and long-term monitoring has the disadvantage of the risk to induce malignancies due to cumulating ionizing radiation exposure. More recently, magnetic resonance imaging (MRI) has emerged as an alternative radiation-free imaging technique for quantitative assessment of CF lung disease. In addition to structural lung damage, chest MRI enables non-invasive assessment of abnormalities in lung perfusion and ventilation characteristically associated with mucus plugging in CF lung disease. Here, we review recent developments and the prospects of MRI for improved and safer imaging with a focus on recent studies that support its utility as a sensitive non-invasive outcome measure of early lung disease in young children with CF. Pediatr Pulmonol. 2016;51:S49-S60. © 2016 Wiley Periodicals, Inc.

Targeting ion channels in cystic fibrosis

Mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene cause a characteristic defect in epithelial ion transport that plays a central role in the pathogenesis of cystic fibrosis (CF). Hence, pharmacological correction of this ion transport defect by targeting of mutant CFTR, or alternative ion channels that may compensate for CFTR dysfunction, has long been considered as an attractive approach to a causal therapy of this life-limiting disease. The recent introduction of the CFTR potentiator ivacaftor into the therapy of a subgroup of patients with specific CFTR mutations was a major milestone and enormous stimulus for seeking effective ion transport modulators for all patients with CF. In this review, we discuss recent breakthroughs and setbacks with CFTR modulators designed to rescue mutant CFTR including the common mutation F508del. Further, we examine the alternative chloride channels TMEM16A and SLC26A9, as well as the epithelial sodium channel ENaC as alternative targets in CF lung disease, which remains the major cause of morbidity and mortality in patients with CF. Finally, we will focus on the hurdles that still need to be overcome to make effective ion transport modulation therapies available for all patients with CF irrespective of their CFTR genotype.

Genetic Deletion and Pharmacological Inhibition of PI3K γ Reduces Neutrophilic Airway Inflammation and Lung Damage in Mice with Cystic Fibrosis-Like Lung Disease

Purpose. Neutrophil-dominated airway inflammation is a key feature of progressive lung damage in cystic fibrosis (CF). Thus, reducing airway inflammation is a major goal to prevent lung damage in CF. However, current anti-inflammatory drugs have shown several limits. PI3Kγ plays a pivotal role in leukocyte recruitment and activation; in the present study we determined the effects of genetic deletion and pharmacologic inhibition of PI3Kγ on airway inflammation and structural lung damage in a mouse model of CF lung disease. Methods. βENaC overexpressing mice (βENaC-Tg) were backcrossed with PI3Kγ-deficient (PI3Kγ^KO) mice. Tissue damage was assessed by histology and morphometry and inflammatory cell number was evaluated in bronchoalveolar lavage fluid (BALF). Furthermore, we assessed the effect of a specific PI3Kγ inhibitor (AS-605240) on inflammatory cell number in BALF. Results. Genetic deletion of PI3Kγ decreased neutrophil numbers in BALF of PI3Kγ^KO/βENaC-Tg mice, and this was associated with reduced emphysematous changes. Treatment with the PI3Kγ inhibitor AS-605240 decreased the number of neutrophils in BALF of βENaC-Tg mice, reproducing the effect observed with genetic deletion of the enzyme. Conclusions. These results demonstrate the biological efficacy of both genetic deletion and pharmacological inhibition of PI3Kγ in reducing chronic neutrophilic inflammation in CF-like lung disease in vivo.

Free DNA in cystic fibrosis airway fluids correlates with airflow obstruction

Chronic obstructive lung disease determines morbidity and mortality of patients with cystic fibrosis (CF). CF airways are characterized by a nonresolving neutrophilic inflammation. After pathogen contact or prolonged activation, neutrophils release DNA fibres decorated with antimicrobial proteins, forming neutrophil extracellular traps (NETs). NETs have been described to act in a beneficial way for innate host defense by bactericidal, fungicidal, and virucidal actions. On the other hand, excessive NET formation has been linked to the pathogenesis of autoinflammatory and autoimmune disease conditions. We quantified free DNA structures characteristic of NETs in airway fluids of CF patients and a mouse model with CF-like lung disease. Free DNA levels correlated with airflow obstruction, fungal colonization, and CXC chemokine levels in CF patients and CF-like mice. When viewed in combination, our results demonstrate that neutrophilic inflammation in CF airways is associated with abundant free DNA characteristic for NETosis, and suggest that free DNA may be implicated in lung function decline in patients with CF.

The role of chitin, chitinases, and chitinase-like proteins in pediatric lung diseases

Chitin, after cellulose, the second most abundant biopolymer on earth, is a key component of insects, fungi, and house-dust mites. Lower life forms are endowed with chitinases to defend themselves against chitin-bearing pathogens. Unexpectedly, humans were also found to express chitinases as well as chitinase-like proteins that modulate immune responses. Particularly, increased levels of the chitinase-like protein YKL-40 have been associated with severe asthma, cystic fibrosis, and other inflammatory disease conditions. Here, we summarize and discuss the potential role of chitin, chitinases, and chitinase-like proteins in pediatric lung diseases.

Airway mucus obstruction triggers macrophage activation and matrix metalloproteinase 12-dependent emphysema

Whereas cigarette smoking remains the main risk factor for emphysema, recent studies in β-epithelial Na(+) channel-transgenic (βENaC-Tg) mice demonstrated that airway surface dehydration, a key pathophysiological mechanism in cystic fibrosis (CF), caused emphysema in the absence of cigarette smoke exposure. However, the underlying mechanisms remain unknown. The aim of this study was to elucidate mechanisms of emphysema formation triggered by airway surface dehydration. We therefore used expression profiling, genetic and pharmacological inhibition, Foerster resonance energy transfer (FRET)-based activity assays, and genetic association studies to identify and validate emphysema candidate genes in βENaC-Tg mice and patients with CF. We identified matrix metalloproteinase 12 (Mmp12) as a highly up-regulated gene in lungs from βENaC-Tg mice, and demonstrate that elevated Mmp12 expression was associated with progressive emphysema formation, which was reduced by genetic deletion and pharmacological inhibition of MMP12 in vivo. By using FRET reporters, we show that MMP12 activity was elevated on the surface of airway macrophages in bronchoalveolar lavage from βENaC-Tg mice and patients with CF. Furthermore, we demonstrate that a functional polymorphism in MMP12 (rs2276109) was associated with severity of lung disease in CF. Our results suggest that MMP12 released by macrophages activated on dehydrated airway surfaces may play an important role in emphysema formation in the absence of cigarette smoke exposure, and may serve as a therapeutic target in CF and potentially other chronic lung diseases associated with airway mucus dehydration and obstruction.

CFTR: cystic fibrosis and beyond

Cystic fibrosis (CF) remains the most common fatal hereditary lung disease. The discovery of the cystic fibrosis transmembrane conductance regulator (CFTR) gene 25 years ago set the stage for: 1) unravelling the molecular and cellular basis of CF lung disease; 2) the generation of animal models to study in vivo pathogenesis; and 3) the development of mutation-specific therapies that are now becoming available for a subgroup of patients with CF. This article highlights major advances in our understanding of how CFTR dysfunction causes chronic mucus obstruction, neutrophilic inflammation and bacterial infection in CF airways. Furthermore, we focus on recent breakthroughs and remaining challenges of novel therapies targeting the basic CF defect, and discuss the next steps to be taken to make disease-modifying therapies available to a larger group of patients with CF, including those carrying the most common mutation ΔF508-CFTR. Finally, we will summarise emerging evidence indicating that acquired CFTR dysfunction may be implicated in the pathogenesis of chronic obstructive pulmonary disease, suggesting that lessons learned from CF may be applicable to common airway diseases associated with mucus plugging.